IMHO, an uncut dome acts as a magnifier for the 'contents' of the weight, and facets basically create 'windows' into the weight. I am not sure why glass artists may choose to cut or not to cut a weight, but personally I think I prefer millefiori weights to be uncut, and lamp-work weights to have 'windows'. I am not sure if other paperweight collectors would agree with me, or if this is a personal preference.